Transistorized voltage regulator



Nov. 29, 1960 B. F. MCNAMEE 2,962,651

TRANSISTORIZED VOLTAGE REGULATOR Filed July 13, 1959 IN VEN TOR.

BEeA/mg E We/1144455 fm wjm United States Patent TRANSISTORIZED VOLTAGE REGULATOR Bernard F. McNamee, Altadena, Califi, assignor to Dresseu-Barnes Corporation, Pasadena, Calif., a corporation of California Filed July 13, 1959', Ser. No. 826,627

8 Claims. (Cl. 323-'22) I If 1 is permitted to flow from the emitter to the base (thence to the collector), it will be amplified in the collector circuit by the current amplification factor B. Upon application of base control current, the collector current rises above BI as a function of the base current, and control is achieved. Thus the collector current comprises an uncontrolled current B1 and a controllable current 1 As long as the load requires current equal to or greater than BI the base current will sufiiciently control the value. A problem obviously arises when the load current is intended to be reduced below the value of H1 In my copending application, Serial No. 757,328, filed August 26, 1958, and entitled Compensating Circuit for Transistor Regulators, now Patent No. 2,912,638, issued November 10, 1959, this general problem is discussed and reference is therein made to the fact that 1 doubles more or less for every IO-degree temperature rise. In said copending application, a preload or bleeder circuit was provided that accommodated BI during conditions of minimum load. Accordingly, the voltage across the load could be held to stable value, and BI would not be compelled to pass through a high impedance load, as would otherwise occur. One basic objective from the standpoint of etiiciency, size of components, etc. is to reduce BI It has been proposed to do this by providing a path for this collector current exclusive of the emitter, namely via the base, so that there will be no internal amplification of this current.

In prior art devices, the path for I via the base has been made substantially preferential as compared to that through the emitter by the aid of a low ohmic value resistor decreasing or minimizing the normal potential difference between the emitter and the base. This arrangement has several serious disadvantages. First of all, a low resistor desensitizes the amplifier of which the transistor forms a part. The previous stage must satisfy not only the normal base to emitter control current, but also the heavy current demands of the resistor that shunt the emitter and base. The previous amplification stage must then handle a substantial amount of power, and problems of heat dissipation and the like arise.

An important object of this invention is to overcome the difficulties above noted. This is accomplished by providing a shunt circuit between the base and emitter that becomes increasingly effective in accordance with its actual need, namely decrease in output current.

Another object of this invention is to provide a comonly handles the minimum collector current, but which ICC also accomplishes variation in effectiveness of the emitter shunt circuit above described.

Another object of this invention is to provide an effective preload circuit that consumes minimal power even under its most active operation.

Another object of this invention is to provide novel circuitry for the foregoing purposes that operates efiectively for variable output regulated power supplies, and during extremes of settings.

Referring to the drawings:

Figure 1 is a circuit diagram of a fixed output power supply incorporating my invention;

Fig. 2 is a circuit diagram for a variable output power supply illustrating a modification of the present invention; and

Fig. 3 illustrates another variable output power supply having unique features with respect to low operating voltages.

In Fig. 1 there is illustrated a transistorized power supply incorporating my invention, and utilizing N-PN transistors by way of example only. An unregulated direct current power supply is indicated by the terminals 10 and 12 at the left of Fig. 1. In the present example, it is assumed desirable to provide a fixed voltage output at terminals 14 and 16.

It will be noted that the plus terminals of the input and output of the system as at 12 and 16 are directly connected together by the aid of a lead 18 to form a common circuit return. A very small ohmic value resis tor is inserted in the lead 18, but the connection between the terminals remains virtually direct. The other terminals 10 and 14 of the input and output are connected together but through an emitter E and a collector C of a transistor Q In practice the transistor Q as it appears in Fig. 1, may be representative of a larger number ganged in order to accommodate the current to the load.

A lead 20 connects the terminal 10 of the unregulated source to the collector C and a lead 22 connects the emitter E to the terminal 14. The transistor Q forms the control element of a series regulator. Thus a change in the conductivity of the transistor Q serves as a means whereby the voltage across the output terminals 14 and 16 is regulated.

Condensers C and C provide a measure of stability at the input and output.

A bridge network 24 senses variations of the voltage across the terminals 14 and 16 from a desired fixed value. An error signal is applied to a lead 26 for purposes of varying the conductance of the series transistor Q5.

In the present example, one branch of the bridge 24 comprises resistor parts R and R for example of a single resistor. The corner junction 28 between the resistor parts R and R rises and falls in accordance with the voltageacross the terminals 14 and 16.

A reference voltage to which the voltage at terminal 28 is compared, is provided on the opposite corner junction 29 of the bridge. This junction 29 is located between a resistor R and a constant voltage drop device in the form of a diode Z The device Z is characterized by the fact that a constant voltage drop exists across it as long as the current is maintained above a critical conduction value. The critical conduction value is conveniently established by connecting the diode Z and resistor R across the output. But it could be provided in other manners, as will appear hereinafter. The junction 29 is thus at a potential fixed with respect to the plus or common return line 18.

A transistor Q serves as a means for producing a signal at the lead 26 in the form of a current, and in accordance with the voltage difference at the junctions 28 and 29. Thus the emitter and base of the transistor Q "are respectively connected to the junctions 29 and 28, and the collector of the transistor Q is connected to the lead 26.

Current fiows from return line 18, diode Z transistor Q lead 26 and to transistor Q and other elements to the minus line 22 through circuits that will presently be described. The normal current through the transistor Q need not be zero, depending upon other conditions of calibration.

The signal at the lead 26 is amplified prior to application to the base B of the series regulating transistor Q For this purpose a transistor Q is provided. The base B of the transistor Q is connected to the lead 26.

The current applied to the transistor Q is amplified at an emitter or output lead 30 of the transistor Q The output lead 30 connects to the input or base B of the series regulating device Q This current is again amplified by the transistor Q to achieve the current necessary to maintain the voltage at the output 14-16 at the desired value. The circuits are, in a well understood manner, designed to apply the error in negative feedback relationship so that an increased error produces increased correction.

To accommodate the minimum leakage current during conditions when the load is intended to be removed, a variable preload circuit is provided. The preload circuit comprises a variable element in the form of a transistor Q and a resistor R The resistor R is connected to the collector C of the transistor Q; at a junction 32. The emitter E of the transistor Q; is connected to the common return line 18, and the terminal of the resistor R remote from the collector C is connected to the minus output lead 14. The resistor R and the collector-emitter circuit for the transistor Q accordingly parallels the output, and provides a bleeder or preload circuit. The preload circuit is capable of accommodating the minimum collector current of the transistor Q In the present example a voltage divider network comprising resistors R and R is placed across the output conveniently to provide biasing voltage for the baseemitter or input circuit of the transistor Q Thus the base B; by the aid of a lead 34 connects to a junction 36 between the resistors R and R which together are placed across the output terminals 1416. Input current thus flows from the return line 18 to emitter E base 13.; to negative source provided at junction 36.

The input circuit for the transistor Q comprises in addition to the resistor R a resistor R of extremely small value, the resistor R being serially inserted in the lead 18. The emitter E which is common to the input and output circuits, is connected to one side of the resistor R whereas the resistor R is connected to the opposite side of the resistor R The resistor R is accordingly included in the input circuit.

In the absence of load current, no voltage drop exists across the resistor R and a predetermined control current is passed between the base B and emitter E due to the biasing voltage at junction 36. This determines a conductivity of the preload circuit quite adequate to accommodate the minimum collector current of the transistor Q As the load increases, the voltage developed across the resistor R by virtue of load current operates to reduce the conductivity of the transistor output circuit. Accordingly, the preload current is squeezed down as the load increases and I is routed elsewhere. In fact the load itself now accommodates and utilizes the minimum collector current. All this is described in my prior application.

If the minimum collector current I can be supplied independently of the emitter E the magnitude of I may be reduced by a factor of where or is the fraction of emitter current which reaches 4 the collector. If on is approximately .96 as may be typical, obviously the magnitude of I may be minimized by a factor of 25. Minimizing I is of course desirable in this example for the reason that the preload circuit may have components drastically reduced both in physical size and power rating.

In order to pass a substantial collector current independently of the emitter E unique use is made of the preload circuit Rq-Q4. A resistor R is connected between the base B of the transistor Q and that end of the resistor R; which adjoins the transistor Q namely, at the junction 32. During conditions of no load, the voltage at the junction 32 is very nearly equal to that at the terminal 16 because the preload circuit is then in a state of high conduction to accommodate the 131 The junction 32 being more positive than the emitter E (which connects to the terminal 14), the path of current to the collector C through R and base B is preferred over the emitter path, and this is true even through the value of the resistance of R is substantial.

When current increases through the main load, the voltage drop across the resistor R reduces the preload current, and the voltage at the terminal 32 now approaches the opposite terminal 14. The preference of collector current for the path via R thus diminishes as the load current increases. Under full load condition, the current through R is reduced, and the collector current now passes through emitter E This is quite acceptable and efiicient since the load now requires current,

and internal amplification of 1 is now no detriment. During high current demand of the main load, resistor R thus does not drain on the output circuit of the transistor Q and efiicient operation is achieved. Thus, the output current from the transistor Q is now used mainly for purposes of driving the input to the transistor Q If all of the minimum leakage current BI were conducted through the preload resistor R and transistor Q the resistor R and Q would have to be of large capacity to handle the maximum BI By using resistor R to carry I and prevent it from being multiplied by B, the maximum current in R can be small, in fact just enough to vary the potential of point 32 so as to change the voltage across R by an amount suificient to force the maximum I of Q through it when the external load current is zero.

In the event that the output voltage of the regulator is to be variable, the resistors R and R of the previous one will not provide a constant biasing potential at the terminal 36 to the base B Accordingly, Fig. 2 illustrates a battery V for providing fixed voltage supply for purposes of satisfactory operation in the event that voltage between leads 18 and 20 varies considerably in accordance with the setting of the device.

The maximum power dissipated in the transistor Q may be kept virtually constant and low for all values of operating voltages by adjusting the relative effect of the transistor output circuit and the resistor R in accordance with change in operating voltage. This is accomplished by the aid of a slider 42 cooperating with one part Rq of the resistor R, that is now made in two parts. A junction 4t? exists between the resistor parts. As the regulated voltage is adjusted upwardly, the slider 42 moves to include more of the resistance R in the preload circuit, maintaining the maximum preload current constant. Appropriate calibration ensures constant maximum power dissipation at the transistor Q The legend Ganged indicates that the slider 42 is shifted by operation of the adjustable control that varies output voltage.

The resistor R which bypasses the current I to the base B is connected to the junction 40. Since the maximum preload current is kept constant by the slider 42, the voltage at junction 40 will be constant for no load conditions, whatever the operating voltage may be. Hence the preference of collector current of transistor Q for the path via R is desirably made independent of operating voltage.

In the form illustrated in Fig. 3, the voltage source V for biasing the transistor Q, is located in the preload circuit itself, that is, between the lead 18 and the emitter E The circuitous effect of the source 44 is obviously equivalent to that illustrated in the previous form, so far as driving input current to the transistor is concerned. In the present form, however, the source V imposes a desirable plus bias upon the junction 40, which ensures preference for the path through R even when the operating voltage is very small. The plus bias on the conjunction 40 drives biasing current in the appropriate direction through the emitter of an N-P-N transistor, and which is used in the present case.

Also illustrated in Fig. 3 is a resistor R which, as R; does for transistor Q provides a path for I of Q that, under no load conditions, is preferred over that via the emitter E The resistor R like resistor R connects to junction 40. Obviously as many preferential circuits can be connected to the preload circuit as desired or necessary.

The inventor claims:

1. In a voltage regulation system having an input and an output, and including a transistor having an emitter and a collector serially coupled to a lead through which load current passes; said transistor having a base forming, with the emitter, an input circuit; means applying a signal to said input circuit for maintaining output voltage at a predetermined value; a preload circuit for absorbing the minimum collector current; means forming a shunt current path between said emitter and base whereby a substantial portion of the collector current flows independently of said emitter; and means for reducing the effectiveness of said shunt circuit upon increase in load current.

2. In a voltage regulation system having an input and an output, and including a transistor having an emitter and a collector serially coupled to a lead through which load current passes; said transistor having a base forming, with the emitter, an input circuit; means applying a signal to said input circuit for maintaining output voltage at a predetermined value; a preload circuit for absorbing the minimum collector current; means providing a terminal, the voltage of which, with reference to said emitter, changes upon decrease in load current; and a resistor between said terminal and said base whereby collector current is substantially supplied via said resistor and independently of said emitter and increasingly upon decreas ing load current.

3. The combination as set forth in claim 2 in which said terminal is provided at a preload circuit, said preload circuit including means for decreasing preload circuit conductivity in response to increased load, said preload circuit including a resistive element across which said voltage is developed.

4. In a voltage regulation system having an input and an output and including: a transistor having an emitter and a collector; a supply line and a return or base line connected between the input and the output of said regulator; the emitter and collector being serially inserted in said supply line; said transistor including a base; means for applying control current between the emitter and the base for maintaining the voltage across the output substantially at a set value; a preload circuit extending between the lines and including a first resistor and a variable conductance element, said preload circuit providing a path for collector current when the load is reduced; means for reducing the preload circuit conductivity upon increase in load current; and a second resistor connected between the base and at least a portion of said first resistor whereby a path via said second resistor for collector current is provided that is increasingly preferential as compared to the emitter upon decrease of load current.

5. In a voltage regulation system having an input and output and including: a first transistor having an emitter and a collector; a supply line and a base or return line, and both extending between the input and the output of the regulator; the emitter and the collector being serially inserted in said supply line; said transistor including a base; means for applying a control current between the emitter and the base for maintaining the voltage across the output at a set value; a preload circuit extending between the supply and return lines, and including a variable resistor, and a second transistor having output electrodes serially joined to the variable resistor, the resistor being connected to the supply line and one of said output terminals being connected to said return line; means for varying the conductance of said second transistor to reduce preload circuit conductivity in response to increased load, comprising an input circuit to said second transistor including an element across which is developed a voltage corresponding to the current in the return line; a second resistor between the base of said first transistor and a fixed part of said first variable resistor to provide a path for the collector current of said first transistor that is increasingly preferential upon decreasing load current; and ganged means for varying the set value of output voltage and for varying the variable resistor whereby the maximum power dissipation in a said second transistor is substantially constant and whereby the voltage developed across the fixed portion of said variable resistor is constant and independent of the output voltage.

6. The combination as set forth in claim 5 in which a source of biasing voltage for the input circuit to said second transistor is common to the output circuit thereof whereby a biasing voltage is provided across said fixed portion of said variable resistor.

7. In a voltage regulation system having an input and an output, and including a transistor having an emitter and a collector serially inserted in a lead through which load current passes; said transistor having a base forming, with the emitter, an input circuit; means, including a second transistor, applying a signal to said input circuit for maintaining output voltage at a predetermined value; a preload circuit for absorbing the minimum collector current; means forming a shunt current path between said emitter and base whereby a substantial portion of the collector current flows independently of said emitter; the second transistor having an emitter, a collector and a base; means forming a shunt path between said emitter and said base of said second transistor whereby a substantial portion of its collector current flows independently of the emitter of said second transistor; and means for reducing the effectiveness of said shunt circuits upon increase in load current.

8. The combination as set forth in claim 2 in which said terminal is provided at a preload circuit including a resistor and a variable circuit element that decreases preload circuit conductivity in response to increased load, the voltage being developed across that portion of said preload circuit resistor between said emitter and said terminal; said preload circuit resistor being capable of carrying a current large enough merely to provide said changing voltage.

No references cited. 

